抄録
The ability of Exorista japonica females to regulate clutch size in response to host density was investigated in the laboratory. On the assumption that the flies can estimate host density by the frequency of host encounters, the effect of time interval between host encounters and the number of hosts offered on the oviposition decision of female flies was studied, and host discriminatory ability was examined. A female fly was offered a cup (considered as a patch) containing host(s) at various time intervals. Clutch size decreased as the time interval between host encounters was shortened and as host density per patch increased. The number of eggs laid per patch during a single attack increased with increases in the time interval between host encounters was lengthened and as host density per patch increased, even at a constant time interval. Females discriminated between unparasitized and parasitized hosts when the parasitized host contained 10 eggs, but did not discriminate when the parasitized host had only 5 eggs. Moreover, the time interval between host encounters affected host discrimination. Females oviposited equally on an unparasitized and a parasitized host with 10 eggs when they encountered hosts at 24 h intervals, but they laid fewer eggs on the parasitized host when the interval between host provisions was 1 min. the results indicated that E. japonica females not only regulated clutch size in relation to host availability but also discriminated between unparasitized and parasitized hosts.
